Figure 1.
(A) The participant sat on a platform that produced continuous roll rotations. Surface electrodes were placed over erector spinae (i.e., ES) and trapezius (i.e., T) muscles. Reflective markers were placed on anatomical landmarks of the upper body and the head and on the platform. (B) Body segments were defined based on the markers’ locations.
Figure 2.
Illustration of data analysis in a pre-walker and an adult.
(A) Typical raw EMGs from erector spinae (ES) and trapezius (T) muscles. The raw signals were then rectified and filtered to obtain envelopes of the EMG patterns. (B) Typical patterns of platform rotation and angular displacements of body segments. (C) Cross-correlation functions between muscle activity or segmental angular displacement and platform rotation. A negative time-lag at the maximum cross-correlation indicates that either the peak of muscle activity or the turning point of segment oscillation precedes the turning point of the platform, and vice versa for a positive-time lag.
Figure 3.
Cross-correlation between muscle activation and platform movement in infants at the pre-walking stage (PW), infants who attained independent walking (W), and young adults.
(A) Lag τ between muscle activation and platform movement. (B) Peak correlation R for muscle activation and platform movement. Data are presented as median (grey mark) and interquartile range (black box). Whiskers extend to the data’s minimum and maximum. Group differences from pairwise multiple comparisons (Dunn’s tests associated with a Bonferroni-Holm correction) are reported using horizontal bars. **: p-value <0.01.
Figure 4.
Cross-correlation between segmental movement and platform movement in walking and non-walking infants and young adults.
(A) Lag τ between segmental movement and platform movement. (B) Peak correlation R for segmental movement and platform movement. Data are presented as median (grey mark) and interquartile range (black box). Whiskers extend to the data’s minimum and maximum. P: pelvis, L: lumbar segment, LT: lower-torso, UT: upper-torso, H: head.
Figure 5.
Normalized lateral displacements of the anatomical markers in infants at the pre-walking stage (pre-walkers), walking infants (walkers), and adults.
Data are presented as median (grey mark) and interquartile range (black box). Whiskers extend to the data’s minimum and maximum. S: sacrum marker, L: lumbar marker, T: thoracic marker, C: cervical marker, H: head marker. Results are illustrated using stick figures (top left corner).
Figure 6.
Angular dispersions of the body segments in infants at the pre-walking stage (pre-walkers), walking infants (walkers), and adults.
Data are presented as median (grey mark) and interquartile range (black box). Whiskers extend to the data’s minimum and maximum. P: pelvis, L: lumbar segment, LT: lower torso, UT: upper torso, H: head.